The present invention relates to a hybrid optical module in which components of an optical pickup, excluding an objective lens are integrated to one another so that the module is miniaturized.
Among devices constituting a CD player, an optical pickup which detects an optical signal is the heart of the CD player. With respect to such an optical pickup, requests for a reduced cost, a high reliability, and a reduced weight have been given. However, a conventional optical pickup which is configured by discrete components cannot meet such requests. Therefore, optical modules of a hybrid configuration which are called a hologram pickup or a laser coupler have begun to be used.
In such hybrid optical modules, particularly in a laser coupler, all parts other than an objective lens are integrated into one component, so as to extremely reduce the size of the module. Specifically, as shown in FIG. 2, a photo diode IC substrate 20 (silicon substrate) on which optoelectric converting elements 22 are formed is used as a base, and a prism and a laser diode 25 are mounted on the base, thereby configuring a laser coupler. The laser coupler is housed in a package which is not shown. An objective lens and mechanical parts such as an actuator are placed on the package to complete an optical pickup unit.
In the figure, the arrows indicate directions of incidence and emission of light. Light emitted from the laser diode 25 is incident on an end face of the prism 24 to change the direction by 90xc2x0, and then converged by an objective lens 26, on a signal plane of an optical disk which is not shown. The light is then reflected with being modulated in intensity by pits, and returns to the prism 24 via the objective lens 26. The optoelectric converting elements (OEICs) 22 detect the light to convert it into an electric signal.
Such a hybrid optical module is housed in a package of the resin type or the metal type. The former type is inferior in mechanical strength and heat resistance. The latter type has difficulties from the viewpoint of a production process, and features which are opposite to requests for reduction in size and weight. In both the types, the above-mentioned hybrid optical module requires the silicon substrate 20 in order to mount the prism 24 and enable the optoelectric converting elements 22 to obtain information of the disk plane. This causes the production cost to be increased.
The invention has been conducted in view of the above-discussed circumstances. It is an object of the invention to provide a hybrid optical module in which a multilayer ceramic substrate is used as the above-mentioned package, a prism serving as a component of an optical pickup unit and a chip on which an optoelectric converting element is mounted are mounted on different layers of the multilayer ceramic substrate to reduce the production cost, and the thickness of the chip on which the optoelectric converting element is mounted is substantially equal to the depth of an arbitrary layer of the multilayer ceramic substrate on which the chip is mounted, whereby wire bonding is facilitated to enhance the workability.
In order to solve the problems discussed above, the hybrid optical module according to a first aspect of the invention is characterized in that a prism which controls incidence and emission angles of light is directly mounted on a multilayer ceramic substrate on which an optoelectric converting element is mounted.
The hybrid optical module according to a second aspect of the invention is characterized in that, in the hybrid optical module according to the first aspect of the invention, the optoelectric converting element is mounted in such a manner that a thickness of the optoelectric converting element itself is substantially equal to a depth of an arbitrary layer of the multilayer ceramic substrate on which the optoelectric converting element is mounted, and the optoelectric converting element is wire-bonded to the arbitrary layer.
According to this configuration, the prism serving as a component of an optical pickup unit and the chip on which an optoelectric converting element is mounted are mounted on different layers of the multilayer ceramic substrate, whereby a silicon substrate is made unnecessary to reduce the production cost. Since the thickness of the chip on which the optoelectric converting element is mounted is substantially equal to the depth of an arbitrary layer of the multilayer ceramic substrate on which the chip is mounted, whereby wire bonding can be facilitated to enhance the workability.